According to a study by NASA, the temperature of the large lakes in the world, including those of the Northern Hemisphere, is increasing on average by 1.23 degree Celsius per decade. A team from the Jet Propulsion Laboratory (JPL), the U.S. space agency, has used satellites to carry out the temperature readings of 167 lakes worldwide, representing over 500 square kilometres.

Because they were unable to make the temperature readings during the season when some of the lakes are covered by ice or hidden by clouds, the NASA researchers focused on temperatures in the summer, from July to September in the northern hemisphere, and from January to March in the Southern Hemisphere.

According to their findings, on average, the temperature on the surface of those 167 lakes has risen by 1.23 degree Celsius per decade, and up to three degrees for those located at the highest latitudes in the Northern hemisphere. Philip Schneider, lead author of the study, however, underlined that "The results have implications for lake ecosystems, which can be adversely affected by even small water temperature changes.” An increase in lake temperature, however small, is sufficient to cause the disruption of their ecosystems. For example, an increase in the temperature of the surface water affects the way in which the deep water mixes with that of the surface, and has a direct impact on aquatic life, which becomes less prolific. In parallel, the same increase in the temperature of the surface water facilitates the growth of algae that in the long term make the lake toxic for fish. As a result, over and above the impact on ecosystems, rising lake temperatures have disastrous economic consequences for local people living mainly from fishing.

The study showed that northern Europe remains the largest area where the warming has been most marked and most consistent. In North America, the rise in temperatures over the last 25 years has been slightly higher in the south-west United States than in the region of the Great Lakes.

This recent analysis by NASA confirms previous studies on the same subject. A study published on 16 May this year also highlighted the disastrous effects of global warming on the second largest lake in the world, Lake Tanganyika in Africa, and on the proliferation of its fish.